1. Field of the Invention
The present invention relates to a filter element composed of a filter bag and a single support cage. More specifically, this invention relates to pulse-jet filter elements, wherein air is directed in a reverse direction to clean the filter elements.
The present invention also relates to star-shaped filter cartridges which include filtration material wound around a perforated inner cylinder.
2. Description of the Prior Art
In the prior art, pulse-jet filter elements have round tubular filter bags, mounted onto tubular wire cages, which have by snap-ring fittings in the housing, where air is drawn through the filter bags during the filtering process and reverse direction air flow through the bags is used to clean the filter bags.
The filter bags are closed on the bottom and open on the top. The dust laden air to be filtered is drawn through the filter bag from outside of the bag and the dust particles are retained on the surface of the filter bag. Air-to-cloth ratio, dust retention and cake-release of a given filter material and the filtration surface determine the efficiency of a fabric-filter pulse-jet bag housing. In this regard, prior art pulse-jet filter bags have been limited by the circumference of the filter bags. Increasing the size of the filter housing in order to increase the circumference of the filter bag and thereby increase the efficiency of the filter typically would result in an expensive and unwieldy filter housing.
Similarly, cartridge filters have the disadvantage of being limited in length, typically not exceeding two meters. They also have limited temperature resistance and a flat folded portion at the ends of the pleated regions which reduces the effective filter area when air is forced through the filter cartridges at high differential pressure.
U.S. Pat. No. 4,259,095 to Johnson has a cage support with a star-like construction, but is constructed to hold a tubular filter bag and was designed to improve the cleaning cycle of pulse-jet filter bags by diffusing the reverse-direction air more efficiently via perforations in the inner tube of the cage support. This inner tube includes peripheral portions extending outwardly beyond other points of the tube for engaging and holding the surrounding filter bag. However, the peripheral portions hold a tubular bag not a star-shaped bag. The inner tube of the cage prevents the cage from being a star-shaped cage to hold a star-shaped bag.
Similarly, U.S. Pat. No. 3,853,509 to Leliaert teaches a tubular filter bag which is held in a star-shape by inner and outer cages. This double cage construction is expensive and time-consuming both in manufacture and installation. This double cage construction is therefore not economically feasible. Additionally, where the filter fabric rests on the tips of the star-rays of the inner cage of the double cage support system of the Leliaert reference forms a point of abrasion to the filtration fabric. This abrasion is caused by the added friction of the outer cage.
Similarly, conical tubes with flanged corners are disclosed in U.S. Pat. No. 2,774,443 to Slayter and British Patent No. 20,176 to Sokal. However, flanges are not filtration surfaces and do not increase the filtration surface of the filter bags.
Other prior art pulse-jet filter elements have a metal support cage to hold them open during the filtration cycle. The cage comprises longitudinal wires or rods welded to wire rings circumferentially spaced along the length of the wires. These cages, possibly as long as eight meters in length, a length which is frequently necessary for the filtration of large volumes of industrial gas, but the long length is disadvantageous during the transportation and installation of filter elements, particularly if there is limited space near the cell plate of the filter housing.